1. Field of the Invention
The present invention relates to a vehicle air conditioner with a hot-gas heater cycle in which an interior heat exchanger is operated as a radiator by introducing hot gas refrigerant from a compressor directly into the interior heat exchanger.
2. Description of Related Art
A conventional vehicle air conditioner, disclosed in JP-A-5-223357 (corresponding to U.S. Pat. No. 5,291,941), performs a hot-gas heating mode using a hot-gas heater cycle in a refrigerant cycle system (hot-gas heating operation). In this conventional vehicle air conditioner, when a temperature of cooling water (hot water) from a vehicle engine to a heater core is lower than a predetermined temperature, for example, when operation of the vehicle engine is started, gas refrigerant discharged from a compressor is introduced directly into an interior heat exchanger while bypassing a condenser. In this case, heat is radiated from gas refrigerant to air in the interior heat exchanger, so that auxiliary heating function can be obtained from the interior heat exchanger relative to hot-water heating function (main heating function) in the heater core. That is, in this conventional vehicle air conditioner, a single interior heat exchanger disposed in an air conditioning case is selectively operated as an evaporator in a cooling mode and as a radiator in the heating mode. For example, the hot-gas heating mode is normally performed in a low outside-temperature area where an outside air temperature is lower than 10 degrees centigrade (° C.). On the other hand, a cooling mode in the refrigerant cycle system is performed not only for cooling a passenger compartment in a cooling operation of the passenger compartment in the summer but also for defrosting a windshield in a heating operation of the passenger compartment in the winter. This cooling mode in the refrigerant cycle system is performed until the outside air temperature is reduced to 0° C., and is stopped in a very low outside-temperature area where the outside air temperature is lower than 0° C.
However, the using areas of the hot-gas heating mode and the cooling mode in the refrigerant cycle system may be overlapped in an outside-temperature area between 0° C. and 10° C. The conventional vehicle air conditioner includes a hot-gas switch and an air conditioning switch which are manually operated by a passenger. When the hot-gas switch is turned on, the hot-gas heating mode is performed in the refrigerant cycle system. On the other hand, when the air conditioning switch is turned on, the cooling mode is performed in the refrigerant cycle system. Here, when any one of the hot-gas switch and the air conditioning switch is once turned on, its turned-on state is maintained until it is again operated. For example, when the air conditioning switch was turned on in the previous operation of a vehicle engine, its turned-on state is maintained. In this case, when the hot-gas switch is turned on in the present operation of the vehicle engine, both the switches are turned on. Accordingly, for example, the cooling mode can be considered to be prior to the hot-gas heating mode, and can be always automatically selected in the refrigerant cycle system. However, in this case, the hot-gas heating mode cannot be performed even in the very low outside-temperature area where the hot-gas heating mode is required.